1. Field of the Invention
The present invention relates to a glass fiber mat for a fiber reinforced plastic material (hereinafter referred to as FRP).
2. Description of the Prior Art
FRP, which is prepared by impregnating a fiber reinforced mat made of a material such as glass fiber with liquid thermosetting resin and curing the resin, has a large mechanical strength and corrosion resistance and is widely used as a structural substrate for various articles such as a tank, a bathtub, a boat, etc. The strength of the FRP depends upon: (1) the kind of fiber reinforced mat and resin forming the FRP; (2) the ratio of the resin to the fiber reinforced mat; (3) the method of molding; and (4) the curing condition of thermosetting resin. Among these elements, the kind of fiber reinforced mat and the ratio of the resin to the fiber reinforced mat highly affect the strength of the FRP. Various proposals for obtaining FRP having a large strength have been known. For example, glass fiber rovings are regularly arranged in one direction to enhance the strength of the mat in that direction. However, such a mat has a disadvantage in that the strength in the direction perpendicular to that direction is inferior.
Normally, the strength of the FRP depends upon the percentage in weight of the fiber reinforced mat in the FRP (this will be referred as GG). A FRP having a large GC can be easily obtained by a press-molding process whereas it is difficult to obtain the FRP having a large GC by a hand-lay-up process. Accordingly, it is difficult to prepare a large article such as a ship with a sufficient strength, because it is difficult to manufacture a ship by press-molding process.
It is possible to obtain FRP having a large GC and a large strength by the hand-lay-up process by using a cloth made of glass fiber rovings (woven roving) as a fiber reinforcing material. The resulting woven roving has disadvantages in that (1) the strength of the woven roving in the biased direction is lower than that of the longitudinal and transversal directions (the direction of roving) and (2) air bubbles are apt to enter into spaces between the glass fibers when the woven roving is impregnated with liquid thermosetting resin and the presence of the air bubbles between the glass fibers causes strength reduction and poor appearance of the FRP.